1. Field of the Invention
The present invention relates to a method of, in a double-side polishing device that polishes by using a polishing pad both sides of a work to be polished such as a wafer or a compact disk which is required to have a mirror-finished surface as well as uniform thickness, grinding (also known as conditioning) the polishing pad that has been clogged with polishing powder and the like after polishing, and, in particular, to a method that can easily grind (condition) the polishing pad. Additionally, the present invention relates to a grinding (conditioning) apparatus which is capable of realizing such a grinding (conditioning) method as described above.
2. Description of Related Art
A wafer is exemplarily shown as a subject to be polished for which uniform thickness and mirror-finished surfaces are required. Both sides of a wafer obtained by thinly cutting single crystal silicon need be precisely mirror-finished and polished to have uniform thickness before semiconductor circuits are formed thereon. For this purpose, as shown in JP 07-009342 Laid-Open, by using a double-side polishing device, a carrier that holds a wafer is sandwiched between an upper and a lower rotating surface plates each having an polishing pad such as felt, while an alkaline solution containing abrasive grains such as silica microparticles is supplied to the polishing pad, and the upper and the lower rotating surface plates are rotated, so that both sides of the wafer are polished to be in a mirror-surface state.
However, in a case where the polishing process is repeated, the polishing pad is impregnated and clogged with a slurry-like product formed by the polishing agent and particles dissociated from the wafer through polishing process, whereby the deterioration of polishing ability of the polishing pad is resulted.
As a method of solving such a problem as described above, JP 07-009342 discloses a cleaning method, comprising the steps of: pressing a grinding plate having diamond or ceramic pellets coated thereon against an polishing pad and rotating the grinding plate, to grind the polishing pad and remove a product of a polishing agent and dissociated wafer particles; and then spraying highly pressurized purified water from a nozzle onto a polished surface of the polishing pad during the polishing operation, to purge the products remaining in a deeper layer of the polishing pad out by an impact of the spraying.
According to the grinding method of JP 07-009342, a grinding plate having a diameter equal to or larger than those of the rotating surface plates is sandwiched between an upper and a lower rotating surface plates and the grinding plate and the rotating surface plates are rotated relative to each other to grind the polishing pad. However, since the degree of clogging with the slurry-like product varies depending on the areas of the polishing pad, there is a possibility that the surface of the polishing pad fails to be uniformly ground after the grinding process by using the grinding plate of JP 07-009342. Consequently, the polishing pad may not be regenerated to an polishing pad having uniform quality after the cleaning process with liquid thereafter and thus polishing of a work surface may not be implemented with high precision.